(CNN) -- Severe weather took only about five minutes to knock out windows and rip signs and awnings off buildings in downtown Bridgeport, Connecticut, Thursday afternoon, eyewitness Beth Bowman reported.

"In seconds it just turned black, and you can't see across the street. There was foggy, crazy hard rain," said Bowman, who was in a downtown bookstore in Bridgeport when the severe weather barreled through.

After five minutes of darkness, the weather cleared and the sun came out, Bowman said. The damage from the brief but powerful storm included uprooted trees and overturned U.S. postal boxes, she said.

Mayor Bill Finch said via Twitter that his city was under a state of emergency.

Weather data showed winds up to 75 mph, said CNN meteorologist Sean Morris. It was not immediately clear if the winds were from a tornado or strong thunderstorm, he said. But the National Weather Service characterized the event as a thunderstorm. It reported wind damage that included "extensive tree damage."

The Bridgeport Police Department said the storm caused significant damage.